No, it depends on the person of course and I think people who aren't "huggers" by nature attach more meaning to them than people who hug regularly. In general they're either a common greeting, a sign of affection, or a way to comfort someone.

I think the only time a hug would ever be sexual (in our culture anyway) is when you're hugging someone you are sexually attracted to. And then any/all physical contact has some kind of erotic undertone to it - at least for one of the people involved.